Systems Analysis and Design in a Changing World, Fifth Edition

1. Systems Analysis and Design in a Changing World, Fifth Edition

2. Systems Analysis and Design in a Changing World, 5th Edition Learning Objectives • Explain how the traditional approach and the object-oriented approach differ when modeling the details of a use case • List the components of a traditional system and the symbols representing them on a data flow diagram • Describe how data flow diagrams can show the system at various levels of abstraction

3. Systems Analysis and Design in a Changing World, 5th Edition Learning Objectives (continued)‏ • Develop data flow diagrams, data element definitions, data store definitions, and process descriptions • Develop tables to show the distribution of processing and data access across system locations

4. Systems Analysis and Design in a Changing World, 5th Edition Overview • What the system does and what event occurs –activities and interactions (use case)‏ • Traditional structured approach to representing activities and interactions • Diagrams and other models of the traditional approach • RMO customer support system example shows how each model is related

5. Systems Analysis and Design in a Changing World, 5th Edition Traditional vs. Object-Oriented Approaches Figure 6-1

6. Systems Analysis and Design in a Changing World, 5th Edition Requirements for the Traditional and OO Approaches Figure 6-2

7. Systems Analysis and Design in a Changing World, 5th Edition Data Flow Diagrams (DFDs)‏ • Graphical system model that shows all main requirements for an IS in one diagram • Inputs/outputs • Processes • Data storage • Easy to read and understand with minimal training

8. Systems Analysis and Design in a Changing World, 5th Edition Data Flow Diagram Symbols Figure 6-3

9. Systems Analysis and Design in a Changing World, 5th Edition DFD Fragment Showing Use Case Look Up Item Availability from the RMO Figure 6-4

10. Systems Analysis and Design in a Changing World, 5th Edition DFD Integrates Event Table and ERD Figure 6-5

11. Systems Analysis and Design in a Changing World, 5th Edition DFD and Levels of Abstraction • Data flow diagrams (DFDs) are decomposed into additional diagrams to provide multiple levels of detail • Higher-level diagrams provide general views of system • Lower-level diagrams provide detailed views of system • Differing views are called levels of abstraction

12. Systems Analysis and Design in a Changing World, 5th Edition Layers of DFD Abstraction for Course Registration System Figure 6-6

13. Systems Analysis and Design in a Changing World, 5th Edition Context Diagrams • DFD that summarizes all processing activity for the system or subsystem • Highest level (most abstract) view of system • Shows system boundaries • System scope is represented by a single process, external agents, and all data flows into and out of the system

14. Systems Analysis and Design in a Changing World, 5th Edition DFD Fragments • Created for each use case in the event table • Represent system response to one event within a single process symbol • Self-contained models • Focus attention on single part of system • Show only data stores required in the use case

15. Systems Analysis and Design in a Changing World, 5th Edition Three Separate DFD Fragments for Course Registration System Figure 6-7

16. Systems Analysis and Design in a Changing World, 5th Edition Event-Partitioned System Model • DFD to model system requirements using single process for each use case/activity in system or subsystem • Combines all DFD fragments together to show decomposition of the context-level diagram • Sometimes called “diagram 0” • Used primarily as a presentation tool • Decomposed into more detailed DFD fragments

17. Systems Analysis and Design in a Changing World, 5th Edition Combining DFD Fragments to Create Event- Partitioned System Model Figure 6-8

18. Systems Analysis and Design in a Changing World, 5th Edition Context Diagram for RMO Customer Support System Figure 6-9

19. Systems Analysis and Design in a Changing World, 5th Edition RMO Subsystems and Use Cases/Activities from Event Table Figure 6-10

20. Systems Analysis and Design in a Changing World, 5th Edition Context Diagram for RMO Order-Entry Subsystem Figure 6-11

21. Systems Analysis and Design in a Changing World, 5th Edition Five Separate DFD Fragments for RMO Order-Entry Subsystem Figure 6-12

22. Systems Analysis and Design in a Changing World, 5th Edition Decomposing DFD Fragments • Most DFD fragments can be further described using structured English • Sometimes DFD fragments need to be diagrammed in more detail • Decomposed into subprocesses in a detailed DFD • DFD numbering scheme • Hierarchical decomposition • DFD Fragment 2 is decomposed into Diagram 2 • Diagram 2 has processes 2.1, 2.2, 2.3, 2.4

23. Systems Analysis and Design in a Changing World, 5th Edition Detailed DFD for Create new order DFD Fragment Figure 6-14

24. Systems Analysis and Design in a Changing World, 5th Edition Physical and Logical DFDs • Logical model • Assumes implementation in perfect technology • Does not tell how system is implemented • Physical model • Describes assumptions about implementation technology • Developed in last stages of analysis or in early design

25. Systems Analysis and Design in a Changing World, 5th Edition Physical DFD for Scheduling Courses Figure 6-15

26. Systems Analysis and Design in a Changing World, 5th Edition Evaluating DFD Quality • Readable • Internally consistent and balanced • Accurately represents system requirements • Reduces information overload – rule of 7 +/- 2 • Single DFD should not have more than 7 +/-2 processes • No more than 7 +/- 2 data flows should enter or leave a process or data store in a single DFD • Minimizes required number of interfaces

27. Systems Analysis and Design in a Changing World, 5th Edition Data Flow Consistency Problems • Differences in data flow content between a process and its process decomposition • Data outflows without corresponding inflows • Data inflows without corresponding outflows • Results in unbalanced DFDs

28. Systems Analysis and Design in a Changing World, 5th Edition Consistency Rules • All data that flows into a process must • Flow out of the process, or • Be used to generate data that flows out of the process • All data that flows out of a process must • Have flowed into the process, or • Have been generated from data that flowed into the process

29. Systems Analysis and Design in a Changing World, 5th Edition Unnecessary Data Input: Black Hole Figure 6-16

30. Systems Analysis and Design in a Changing World, 5th Edition Process with Impossible Data Output: a Miracle معجزة Figure 6-17

31. Systems Analysis and Design in a Changing World, 5th Edition Process with Unnecessary Data Input Figure 6-18

32. Systems Analysis and Design in a Changing World, 5th Edition Process with Impossible Data Output Figure 6-19

33. Systems Analysis and Design in a Changing World, 5th Edition Documentation of DFD Components • Lowest-level processes need to be described in detail • Data flow contents need to be described • Data stores need to be described in terms of data elements • Each data element needs to be described • Various options for process definition exist

34. Systems Analysis and Design in a Changing World, 5th Edition Structured English • Method of writing process specifications • Combines structured programming techniques with narrative English • Well-suited for lengthy sequential processes or simple control logic (single loop or if-then-else)‏ • Ill-suited for complex decision logic or few (or no) sequential processing steps

35. Systems Analysis and Design in a Changing World, 5th Edition Structured English Example Figure 6-20

36. Systems Analysis and Design in a Changing World, 5th Edition Process 2.1 and Structured English Process Description Figure 6-21

37. Systems Analysis and Design in a Changing World, 5th Edition Decision Tables and Decision Trees • Can summarize complex decision logic better than structured English • Incorporate logic into the table or tree structure to make descriptions more readable

38. Systems Analysis and Design in a Changing World, 5th Edition Decision Table for Calculating Shipping Charges Figure 6-23

39. Systems Analysis and Design in a Changing World, 5th Edition Decision Tree for Calculating Shipping Charges Figure 6-24

40. Systems Analysis and Design in a Changing World, 5th Edition Data Element Definitions • Data type description • String, integer, floating point, Boolean • Sometimes very specific written description • Length of element • Maximum and minimum values • Data dictionary – repository for definitions of data flows, data stores, and data elements

41. Systems Analysis and Design in a Changing World, 5th Edition Data Element Definition Examples Figure 6-30

42. Systems Analysis and Design in a Changing World, 5th Edition Components of a Traditional Analysis Model Figure 6-31

43. Systems Analysis and Design in a Changing World, 5th Edition Summary • Data flow diagrams (DFDs) are used in combination with event table and entity-relationship diagram (ERD) to model system requirements • DFDs model system as set of processes, data flows, external agents, and data stores • DFDs easy to read – graphically represent key features of system using small set of symbols • Many types of DFDs – context diagrams, DFD fragments, subsystem DFDs, event-partitioned DFDs, and detailed process DFDs

44. Systems Analysis and Design in a Changing World, 5th Edition Summary (continued)‏ • Each process, data flow, and data store requires detailed definition • Analyst may define processes as structured English process specifications, decision tables, decision trees, or detail process DFDs • Detailed process decomposition DFDs used when internal process complexity is great • Data flows are defined by component data elements and their internal structure (algebraic notation)‏